726. The Panchromatic Plate

The Panchromatic Plate. Orthochromatic photography is the means by which we obtain, with the aid of properly prepared plates, the light intensity values of objects not obtained by the use of the ordinary dry plate, commonly used in photographic work.

727. Orthochromatic, from the Greek words, Orthos = correct, and Chroma = color.

728. The Panchromatic plate, a late addition to the utilities in the field of orthochromatic photography, is so prepared that it is sensitive, in almost a like degree, to all colors under certain condition, i. e., in combination with various color screens.

729. One must not, however, form the impression that color contrasts can be rendered, but it makes possible the recording in monochrome, contrasts of light and shade in proportionate intensities as seen by the naked eye. This in turn requires that we determine the predominating color, and select the screen that will give to that particular color and minor surrounding colors, the best value as to their light and shade.

730. The extreme sensitiveness of this plate to the various colors make it valuable in connection with the Three-color Process which, as is well known, requires that three separate negatives be made, termed the Red, Blue and Yellow plates, necessitating the use of three separate color screens, green, red, and violet.

731. Development

Development. Due to its sensitiveness, the Panchromatic plate should be developed in total darkness for from five to six minutes (according to the density required in the negative).

Formula.

By Weight.

A. -

Pure Water..........

16 ounces

Pyrogallic Acid..........

1 ounce

Oxalic Acid...........

10 grains

B.-

-Pure Water...........

16 ounces

Sulphite of Soda ......

2 ounces

C-

- Pure Water.............

16 ounces

Carbonate of Soda........

2 ounces

Use A I ounce; B I ounce; C I ounce; Pure Water, 7 ounces.

By Hydrometer Test.

A.-

-Pure Water.........

16 ounces

Pyrogallic Acid...........

1 ounce

Oxalic Acid.........

10 grains

B. - Sulphite of Soda, Solution Test sixty degrees.

C. - Carbonate of Soda, Solution Test fifty degrees.

Use A 1 ounce; B 1 ounce; C 1 ounce; Pure Water, 7 ounces.

Note. - Extreme softness, or low tone values, may be had by diluting the normal developer and increasing the time of development accordingly.

A fresh fixing solution should be used in order that the plates are free from all stains.

After fixing they may be handled in the usual manner.